An illumination optical system having a more simplified structure forms
various quadrupole-shaped secondary light sources with two-time
rotational symmetry with respect to an optical axis. The apparatus can
provide illumination conditions that differ in two perpendicular
directions on a radiation-receiving plane. In order to form a secondary
light source with a quadrupole-shaped light intensity distribution on an
illumination pupil plane, a diffractive optical device is provided in
which an entrance light beam is converted into four light beams, and a
light beam having a shape of four points centered about the optical axis
is formed in a far field. The diffractive optical device is provided with
a first diffractive optical member that is rotatable about a first axis
parallel to the optical axis, and a second diffractive optical member
that is rotatable about a second axis parallel to the optical axis, and
that is arranged adjacent to the first diffractive optical member. A
refractive optical device having first and second refractive optical
members accomplishes similar results.